Windmills have been used for many generations for the purpose of pumping water from the ground and for generating electricity. A basic advantage of the windmill is that it uses the power of atmospheric wind to rotate a wheel having radially extending blades. This rotary movement may be converted into various useful purposes. For example, wind turbines in the form of propellers mounted on towers have been placed in areas where steady winds are prevalent and the wind turbines are used to generate electricity. An electrical generator usually is positioned near the axis of rotation of the propellers, adding the weight of the generator to the upper portion of the mast of the assembly The blades of the conventional large wind turbines are large and made of expensive rigid material and are constructed to have the blades extend radially from a central hub, with no extra support at the outer tips of the blades. The conventional wind turbine blades rotate at a high rate of revolutions and must withstand both the centrifugal forces generated by the fast revolution of the blades and the cantilever bending forces applied to the blades by the wind. Since the outer portions of the blades usually move at a very high velocity and are engaged by strong winds, the larger the blades the stronger they must be and the more expensive they become. Thus, there is a practical limit as to the length and width of the blades.
Another wind turbine type has rigid propellers that appear to be rigidly mounted to circular perimeter rims that support the outer ends of the propellers, as shown in U.S. Pat. Nos. 1,233,232 and 6,064,123. Rubber tires or other rotary objects are placed in positions to engage the outer rim so as to rotate the rubber tires, with the driven tires rotating the rotor of a generator. Thus, the rotation of the wind turbine is used to generate electricity.
The perimeter rim of a large wind turbine is likely to rotate in an irregular circular path so that at one position about the path of the rim the rim appears to wobble in an axial direction, parallel to the axis of rotation of the turbine wheel. This irregular rotation may be caused by several conditions, such as by wind turbulence, a change in wind velocity, equipment vibration, changes in wind direction, and imprecise formation and/or warping of the perimeter rim and its supporting structure. The larger the diameter of the wind turbine, the more likelihood of rotation of the rim in an irregular path and the more likelihood of greater amplitude of the axial displacement of the irregular movement of the perimeter rim.
One of the advantages of a turbine wheel with a perimeter rim is that the electrical generator(s) may be positioned at the rim at the lower arc of rotation of the rim where the generators are closer to the ground or other low supporting surface to remove the weight of the generator from the upper portion of the mast. Also, the position of the generator at a rim of the turbine wheel gives more access for installation, maintenance, repair and replacement of the generator. However, if the perimeter rim of the wind turbine wobbles during operation, it may be difficult to maintain the generator in proper alignment with the rim and it appears likely that stress between the generator and the turbine wheel will occur. Also, if multiple ones of the generators are placed in operative locations about an arc of the rim of the turbine, the potential problems caused by the wobbling rim appear likely to be more prevalent.
While is desirable to make a wind turbine that does not wobble during rotation, from a practical viewpoint it is likely that even the more perfect wind turbines will wobble to some extent when rotating. Accordingly, it would be desirable to have a connection between the rim of a wind turbine and one or more electrical generators that accommodates the rotation of the rim when the rim tends to wobble in an axial direction.